The invention relates to an apparatus for supplying a shingled or overlapping sheet stream from a stack of sheets of a sheet feeder to a feed table of a sheet-processing machine.
Such devices are generally known. The sheets, segregated from a stack of sheets by a sheet feeder, are transported as a shingled or overlapping sheet stream on a belt table having suction belts, are taken hold of there by the suction belts and are transported to the feed table. At the same time, in the region where the sheets are taken over, the suction belts are acted upon with a negative pressure by a suction chamber facing the sheet feeder. At the same time, in the region of sheet transfer on the feed table, the suction belts are acted upon with negative pressure by a suction chamber facing the machine. The front sheet of the sheet stream is guided on the feed table with the front edge against front guide stop and thus is aligned with the font edge. Subsequently, the sheet is aligned, for example, with the side edge. During the alignment of the front sheet, the latter must be guided by the suction belt by a holding force, so that the front edge is not damaged while the sheet is fed to the front guide stop and thus lateral alignment is possible without problems. This becomes feasible owing the fact that, due to the under-shingled subsequent sheet, the suction belts are covered completely or almost completely, so that the sheet, which is to be aligned, is guided only with a slight holding force in the transfer region. If there is no subsequent sheet, for example, when the sheet stream is interrupted, the holding force acting on the last sheet to be aligned, during the processing of paper, presents a potential danger of damage to the front end of the sheet and an accurate lateral alignment is not possible.
In order to eliminate this disadvantage, it is proposed in EP 0 554 774 B1 that the supplying of the last sheet of the sheet stream be detected. When the final sheet in the stream reaches the alignment end, the supply of negative pressure to the suction chamber facing the machine is interrupted and this suction chamber is connected with a source of positive pressure. This device cannot be used for thin printing paper, since there is no defined guiding of the last sheet to the front guide stop.